1. Field of the Invention
The present invention relates to a fuzzy inference operation method and a device therefor, and particularly relates to a fuzzy inference operation method enabling reduced operation time for MIN and MAX value operations and a device therefor.
2. Description of the Prior Art
A conventional fuzzy inference operation device using the MIN-MAX method is illustrated in FIGS. 4 to 6 and comprises a membership value determination means which determines the membership value for condition parts referring to condition part membership functions (a) 401, (b) 403 and (c) 405 according to singleton input variables 402, 404 and 406 as shown in FIGS. 4A, 4B and 4C, a MIN value operation means which compares two or more condition part membership values to take the smaller one as the result as shown in FIG. 4E, and a MAX value operation means which compares two or more membership values or the results of MIN value operations (a) 501, (b) 502 and (c) 503 as shown in FIGS. 5A, 5B and 5C to take the largest one as the MAX value operation result 504. It is also provided with rules specifying which condition part membership function is to be referred to by a singleton input variable for determination of the membership value, which membership value is used for MIN value operation and which conclusion part membership function 407 as shown in FIG. 4D is kept.
Now, referring to FIG. 6, the fuzzy inference operation processing according to the MIN-MAX method is described. The conclusion number is supposed to be 1 here.
The variable c is set to 0 (Step 601). The condition part membership value is determined by referring to the condition part membership function as specified by the rules corresponding to the singleton input variable as shown in FIGS. 4A, 4B and 4C (Step 602). A MIN value operation is executed for the condition part membership value as specified by the rules (Step 603). Another MIN value operation is executed for the result from the MIN value operation 603 and the conclusion part membership function (Step 604). The result of the MIN value operation 604 and the result of the previous MAX value operation 605 are subjected to a MAX value operation (Step 605). Steps 602 to 605 are executed for a number of times equal to the number of rules (Step 606).
As described above, the conventional fuzzy inference operation using the MIN-MAX method comprises the first MIN value operation for the condition part membership value (Step 603 in FIG. 6), the second MIN value operation using the result of the MIN value operation and the conclusion part membership function (Step 604 in FIG. 6) and the MAX value operation using the result of the preceding MIN value operation and the result of the MAX value operation according to the previous rule (Step 605 in FIG. 6).
Referring to FIG. 4, when any of the condition part membership values is the minimum value .mu.-min which is the smallest value a membership value can take (FIG. 4A), the result of the second MIN value operation becomes the minimum value .mu.-min, and the membership value as a result of the second MIN value operation is the minimum value .mu.-min for the entire range. In this case, the rules do not affect the operation result, with the results of the first and the second MIN value operations (Steps 603 and 604 in FIG. 6) and the MAX value operation (Step 605 in FIG. 6) unused. This means that the operation is prolonged by useless processes.